Oklahoma Tornado Alert Gave Residents 36 Minutes Warning

Piles of debris lie around a home destroyed by a tornado in Moore, Oklahoma. Photographer: Brett Deering/Getty Images

May 22 (Bloomberg) -- Residents of Moore had about 36
minutes to prepare for a mile-wide tornado that flattened the
Oklahoma City suburb, killing two dozen people, according to the
National Weather Service.

The federal agency issued its first warning for residents
to seek shelter at 2:40 p.m. local time on May 20, 16 minutes
before the tornado touched down about 10 miles (16 kilometers)
west of the city, said David Andra, a National Weather Service
meteorologist in Norman, Oklahoma. The twister reached Moore at
3:16 p.m., he said, topping the service’s scale for tornadoes
with winds of more than 200 miles per hour.

“A 36-minute time period is pretty substantial,” Andra
said in an interview. The average lead time for tornado warnings
is 14 minutes, according to the National Oceanic and Atmospheric
Administration.

Tornadoes are nature’s most violent storms and can develop
so rapidly that little, if any, advance warning is possible,
according to the Federal Emergency Management Agency. Government
officials and researchers credit early warnings with saving
lives by giving people time to get to shelters.

“Advanced notice is very important,” said John Trostel,
director of the Severe Storms Research Center at the Georgia
Tech Research Institute in Atlanta. “That is why, even with
such a massive scale of destruction, we are seeing tens of
casualties instead of hundreds.”

Activate Alert

The National Weather Service said in its May 20 warning
that people in the affected area should “take cover now in a
storm shelter or an interior room of a sturdy building. Stay
away from doors and windows.”

Moore doesn’t maintain any community storm shelters and
instead instructs residents to shelter in place in a resilient
structure, calling that the best way to stay safe from a fast-approaching tornado, according to the city’s website.

It’s up to Oklahoma cities to activate alert systems once
the National Weather Service issues a tornado warning, said
Terri Watkins, a spokeswoman for the state Emergency Management
Department.

Moore sounded its 36 tornado sirens three times before the
twister hit, according to its Facebook page. In three postings
on the page, the city warned residents that the sirens were
sounding and said to take shelter and follow precautions.

Moore didn’t activate its “code red” mass notification
system, said Jayme Shelton, a spokesman for the city. The system
dials phone numbers, plays a recorded message and sends e-mail
and text messages, according to an emergency operations plan
published in September.

Multiple Alerts

Asked why the city didn’t use the phone and e-mail system,
Shelton said the sirens are more effective.

Moore was among the first cities certified as
“StormReady” by the National Weather Service in 2001. The
designation, which Moore renewed last year, requires a
government to have multiple ways to alert residents.

In addition to the city’s warnings, forecasters, private
groups and individuals sent alerts on the Internet.

The American Red Cross sent warnings through a new
smartphone application that tells users of approaching
tornadoes, according to Melanie Pipkin, a spokeswoman for the
Washington-based group.

In a posting on the social-media service Twitter, the
National Weather Service wrote: “The tornado is so large you
may not realize it’s a tornado. If you are in Moore, go to
shelter NOW!” The message was resent by users about 150 times.

Radar Advances

The average lead time for tornado warnings was 5 minutes in
the early 1990s, said Lans Rothfusz, deputy chief of warning
research and development at the National Severe Storms
Laboratory in Norman. Advances in radar have helped forecasters
by showing how rapidly air is rotating and whether debris is
being carried in a storm, both indicators of a tornado, he said.

Computer forecasting models a decade away from deployment
may provide as much as an hour’s notice, Rothfusz said. Instead
of relying on radar to spot a storm, the models would predict
tornadoes based on weather patterns.